1. Field of Use
This invention relates generally to modulatable power transmission clutches and, in particular, to those wherein a fluid-applied spring release piston operates on clutch plates which are disposed between a rotatable driving member and a rotatable driven member to effect clutch modulation.
2. Description of the Prior Art
Each of the following U.S. patents has been assigned to an assignee common with the present application.
U.S. Pat. No. 4,451,238, issued May 29, 1984 to Arnold, discloses a multi-clutch transmission with forward and reverse shafts and gear trains between these shafts, and discusses the damaging shocks to the propulsion system which sometimes occur during maneuvering operations.
U.S. Pat. No. 4,459,873, issued Jul. 17, 1984 to Black, shows a marine propulsion system and discusses a brake which is engaged to anchor a portion of the planetary gear system to drive the propeller in a forward direction, and the brake is disengaged when the torque converter is driving the propeller shaft in the reverse direction. This patent discusses prior art transmissions, which were not always satisfactory because of flutter failure of the forward drive clutch, when it was required to operate in the reverse direction for reversing the direction of the boat.
U.S. Pat. No. 4,836,809, issued Jun. 6, 1989 to Pelligrino, discloses a marine vessel propulsion system having forward and reverse clutches in which each clutch can be fully engaged, fully disengaged, and modulated.
U.S. Pat. No. 4,186,829, issued Feb. 5, 1980 to Schneider and Pelligrino, discloses a modulatable power transmission clutch. This patent discloses a spring biased trigger valve, which is located radially outwardly of the central power transmission shaft on which the clutch is mounted.
The present invention provides a modulatable power transmission clutch and also a marine transmission system for variable speed control having dual area clutch pistons. Clutch capacity is varied by separate fluid areas of the clutch, one area being smaller than the other. The marine transmission clutch is modulated by means of the small area of the piston utilizing a selectively operable control resulting in variable propeller speed. Pressure fluid is supplied to the small area by controlling a proportional valve. Modulation of the clutch offers enhanced docking control and vessel positioning. At a predetermined pressure level at the source area of the piston, a spring biased trigger valve allows the flow of pressure fluid to the large area of the piston whereby the clutch can reach full clutch capacity. The system offers seamless transition from modulating operation of the clutch where engine speed can be increased slightly to full engagement of the clutch.
The dual area clutch provided by the present invention provides smooth transition from the initial docking mode and provides for precise and rapid back and forth changes in speed for maneuvering in the docking procedure. The valve of the present invention is located in the central power transmission shaft that extends through the clutch, is much less complicated than the valves of the prior art, and is not affected by centrifugal pressure.
These and other objects and advantages of the invention will appear as this disclosure progresses.